This invention relates to a frequency responsive switching circuit. More particularly, the invention relates to a frequency responsive switching circuit that may be used to produce a switched signal when the RPM of a rotating shaft, such as the crankshaft of a vehicle engine, reaches a predetermined level. Hysteresis may be provided to change the RPM level at which the circuit output is switched once again to its original condition.
The present invention may be used in an engine control system such as that described in my concurrently filed and commonly assigned patent application Ser. No. 716,865, filed Aug. 23, 1976 and entitled "Circuit for Controlling the Operability of One or more Cylinders of a Multicylinder Internal Combustion Engine."
There are numerous situations in which it is desired to provide a switched output signal when the frequency of a periodically varying parameter has reached a predetermined level or fallen below such level. An example of another frequency responsive switching circuit utilized in this manner is described in U.S. Pat. No. 3,914,619, issued Oct. 21, 1975 to Dennis D. Talmage et al. The circuit described in the above patent is utilized in controlling the position of a throttle mechanism on an internal combustion engine.